Head-mounted display device and control method for the head-mounted display device

ABSTRACT

A head-mounted display device includes: an image-light generating unit for right eye that generates image light from image data for right eye and emits the image light; an image-light generating unit for left eye that generates image light from image data for left eye and the image light; a light guide units that guide the emitted image lights to the left and right eyes of the user; and a display control unit that transmits control signals for controlling the emission of the image lights respectively to the image-light generating unit for right eye and the image-light generating unit for left eye. The display control unit transitions, according to a condition set in advance, the head-mounted display device to a power saving state for causing one of the image-light generating unit for right eye and the image-light generating unit for left eye to stop the emission of the image light.

This is a continuation application of application Ser. No. 13/351,492filed Jan. 17, 2012 which claims priority to JP2011-026810 filed Feb.10, 2011 and JP2011-026809 filed Feb. 10, 2011. The disclosures of theprior application are hereby incorporated by reference herein in theirentirety.

BACKGROUND

1. Technical Field

The present invention relates to a head-mounted display device, which isa display device mounted on the head, and a control method for thehead-mounted display device.

2. Related Art

There is known a head-mounted display device (a head mounted display,HMD), which is a display device mounted on the head. For example, thehead-mounted display device generates image light representing an imageusing a liquid crystal display and a light source and guides thegenerated image light to the eyes of a user using a projection opticalsystem and a light guide plate to thereby cause the user to recognize avirtual image. In general, in the head mounted display, a configurationcapable of being battery-driven is adopted in order to improveportability. The battery-driven head mounted display is requested toreduce power consumption of the head mounted display in order toincrease an available time. In this regard, in the past, there is knowna technique for realizing a reduction in power consumption of the headmounted display by reducing the resolution or the frame rate of an imageformed on a display device (see, for example, JP-A-2009-118159).However, when the resolution or the frame rate of the image formed onthe display device is reduced, the image quality of a virtual imagerecognized by the user is markedly deteriorated.

SUMMARY

An advantage of some aspects of the invention is to provide a techniquefor realizing low power consumption without deteriorating the imagequality of a virtual image recognized by a user.

Application Example 1

This application example of the invention is directed to a head-mounteddisplay device that causes a user to recognize a virtual image in astate in which the head-mounted display device is mounted on the head ofthe user. The head-mounted display device includes: an image-lightgenerating unit for right eye that generates image light from image datafor right eye corresponding to the right eye of the user and emits theimage light; an image-light generating unit for left eye that generatesimage light from image data for left eye corresponding to the left eyeof the user and emits the image light; a pair of light guide units thatguide the image lights, which are emitted from the image-lightgenerating unit for right eye and the image-light generating unit forleft eye, to the left and right eyes of the user; and a display controlunit that transmits control signals for controlling the emission of theimage lights respectively to the image-light generating unit for righteye and the image-light generating unit for left eye. The displaycontrol unit transitions, according to a condition set in advance, thehead-mounted display device to a power saving state for causing one ofthe image-light generating unit for right eye and the image-lightgenerating unit for left eye to stop the emission of the image light andcausing the other to execute the emission of the image light.

With such a configuration, the display control unit transitions,according to the condition set in advance, the head-mounted displaydevice to the power saving state for causing one of the image-lightgenerating unit for right eye and the image-light generating unit forleft eye to stop the emission of the image light and causing the otherto execute the emission of the image light. Therefore, in thehead-mounted display device, it is possible to realize a reduction inpower consumption without deteriorating the image quality of a virtualimage recognized by the user.

Application Example 2

This application example of the invention is directed to thehead-mounted display device of Application Example 1, wherein thecondition set in advance is a condition that a target image used fordisplay of the virtual image is a still image. With such aconfiguration, in the head-mounted display device, it is possible torealize a reduction in power consumption when the target image is astill image.

Application Example 3

This application example of the invention is directed to thehead-mounted display device of Application Example 1 or 2, which furtherincludes a battery that supplies electric power to the head-mounteddisplay device. The condition set in advance is a condition that theremaining power of the battery is equal to or smaller than predeterminedremaining power. With such a configuration, in the head-mounted displaydevice, it is possible to realize a reduction in power consumption whenthe remaining power of the battery is equal to or smaller than thepredetermined remaining power.

Application Example 4

This application example of the invention is directed to thehead-mounted display device of any of Application Examples 1 to 3, whichfurther includes an illuminance acquiring unit that acquires illuminanceindicating ambient brightness. The condition set in advance is acondition that the acquired illuminance is equal to or lower thanpredetermined illuminance.

With such a configuration, in the head-mounted display device, it ispossible to realize a reduction in power consumption when illuminance isequal to or lower than the predetermined illuminance.

Application Example 5

This application example of the invention is directed to thehead-mounted display device of any of Application Examples 1 to 4, whichfurther includes: a temperature detecting unit for right eye thatdetects the temperature of the image-light generating unit for righteye; and a temperature detecting unit for left eye that detects thetemperature of the image-light generating unit for left eye. Thecondition set in advance is a condition that at least one of thetemperature detected by the temperature detecting unit for right eye andthe temperature detected by the temperature detecting unit for left eyeis equal to or higher than predetermined temperature. With such aconfiguration, in the head-mounted display device, it is possible torealize a reduction in power consumption when at least one of thetemperature of the image-light generating unit for right eye and thetemperature of the image-light generating unit for left eye is equal toor higher than the predetermined temperature.

Application Example 6

This application example of the invention is directed to thehead-mounted display device of any of Application Examples 1 to 5,wherein the condition set in advance is any one of a condition that thehead-mounted display device detects startup of an application designatedin advance in an operating system installed in the head-mounted displaydevice, a condition that the head-mounted display device acquires arequest from the outside, and a condition that the head-mounted displaydevice detects that a state in which operation for the head-mounteddisplay device is not detected continues for a predetermined time.

With such a configuration, in the head-mounted display device, it ispossible to realize a reduction in power consumption when thehead-mounted display device detects the startup of the applicationdesignated in advance in the operating system installed in thehead-mounted display device, when the head-mounted display deviceacquires a request from the outside, or when the head-mounted displaydevice detects that the state in which operation for the head-mounteddisplay device is not detected continues for the predetermined time.

Application Example 7

This application example of the invention is directed to thehead-mounted display device of any of Application Examples 1 to 6, whichfurther includes a selection receiving unit that receives, from theuser, selection of one of the image-light generating unit for right eyeand the image-light generating unit for left eye, the emission of theimage light from which is stopped by the display control unit.

With such a configuration, the head-mounted display device includes theselection receiving unit that receives, from the user, selection of oneof the image-light generating unit for right eye and the image-lightgenerating unit for left eye, the generation and the emission of theimage light from which are stopped by the display control unit.Therefore, it is possible to improve convenience.

Application Example 8

This application example of the invention is directed to thehead-mounted display device of any of Application Examples 1 to 7,wherein the display control unit alternately switches, in the powersaving state, a first state for causing one of the image-lightgenerating unit for right eye and the image-light generating unit forleft eye to stop the emission of the image light and causing the otherto execute the emission of the image light and a second state forcausing one of the image-light generating unit for right eye and theimage-light generating unit for left eye to execute the emission of theimage light and causing the other to stop the emission of the imagelight.

With such a configuration, the display control unit alternatelyswitches, in the power saving state, the first state for causing one ofthe image-light generating unit for right eye and the image-lightgenerating unit for left eye to stop the emission of the image light andcausing the other to execute the emission of the image light and thesecond state for causing one of the image-light generating unit forright eye and the image-light generating unit for left eye to executethe emission of the image light and causing the other to stop theemission of the image light. Therefore, in the head-mounted displaydevice, it is possible to realize a reduction in power consumptionwithout deteriorating the image quality of a virtual image recognized bythe user.

Application Example 9

This application example of the invention is directed to thehead-mounted display device of Application Example 8, wherein, inswitching the first state and the second state, the display control unitswitches the first state and the second state through a third state forcausing both the image-light generating unit for right eye and theimage-light generating unit for left eye to execute the emission of theimage lights. With such a configuration, when the display control unitswitches the first state and the second state, the display control unitswitches the states through the third state for causing both theimage-light generating unit for right eye and the image-light generatingunit for left eye to execute the emission of the image lights.Therefore, it is possible to more naturally switch the first state andthe second state.

Application Example 10

This application example of the invention is directed to thehead-mounted display device of Application Example of 8 or 9, whereinthe display control unit switches the first state and the second statefurther includes: a temperature detecting unit for right eye thatdetects the temperature of the image-light generating unit for righteye; and a temperature detecting unit for left eye that detects thetemperature of the image-light generating unit for left eye. The displaycontrol unit switches the first state and the second state when adifference between the temperature detected by the temperature detectingunit for right eye and the temperature detected by the temperaturedetecting unit for left eye is equal to or larger than a predeterminedtemperature difference.

With such a configuration, the display control unit switches the firststate and the second state when a difference between the temperature ofthe image-light generating unit for right eye and the temperature of theimage-light generating unit for left eye is equal to or larger than apredetermined temperature difference. Therefore, it is possible tosuppress a rise in the temperature of one of the image-light generatingunits.

Application Example 11

This application example of the invention is directed to thehead-mounted display device of any of Application Examples of 1 to 10,which further includes an image processing unit that acquires a targetimage used for display of the virtual image and generates the image datafor right eye and the image data for left eye using the target image.

The invention can be implemented in various forms. For example, theinvention can be implemented in forms such as a head-mounted displaydevice and a control method for the head-mounted display device, ahead-mounted display system, a computer program for realizing functionsof the method, device, or the system, and a recording medium havingrecorded therein the computer program.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is an explanatory diagram showing an external configuration of ahead-mounted display device in a first embodiment of the invention.

FIG. 2 is a block diagram functionally showing the configuration of ahead mounted display.

FIG. 3 is an explanatory diagram showing an example of a virtual imagerecognized by a user.

FIG. 4 is a state transition diagram showing states that the headmounted display could take.

FIG. 5 is a flowchart for explaining a procedure of processing performedwhen the head mounted display transitions to a normal state.

FIGS. 6A and 6B are explanatory diagrams showing a state in which imagelight is emitted through the processing shown in FIG. 5.

FIG. 7 is a flowchart for explaining a procedure of processing performedwhen the head mounted display transitions to a power saving state.

FIGS. 8A and 8B are explanatory diagrams showing states of image-lightgenerating units at a point when processing in step S202 in FIG. 7 ends.

FIGS. 9A to 9C are explanatory diagrams showing an example of statetransition of the head mounted display.

FIG. 10 is a state transition diagram showing states that a head mounteddisplay in a second embodiment could take.

FIG. 11 is a flowchart for explaining a procedure of processingperformed when the head mounted display in the second embodimenttransitions to a second state.

FIGS. 12A and 12B are explanatory diagrams showing states of image-lightgenerating units at a point when processing in step S302 in FIG. 11ends.

FIGS. 13A and 13B are explanatory diagrams showing an example of statetransition of the head mounted display in the second embodiment.

FIG. 14 is a state transition diagram showing states that a head mounteddisplay in a third embodiment could take.

FIGS. 15A to 15C are explanatory diagrams showing an example of statetransition of the head mounted display in the third embodiment.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Embodiments of the invention are explained below.

A. First Embodiment A-1. Configuration of a Head-Mounted Display Device

FIG. 1 is an explanatory diagram showing an external configuration of ahead-mounted display device in a first embodiment of the invention. Ahead-mounted display device HM is a display device mounted on the headand is also called head mounted display (HMD). The head mounted displayHM in this embodiment is an optical transmissive head-mounted displaydevice 30 with which a user can visually recognize a virtual image andat the same time directly visually recognize an external scene.

The head mounted display HM includes an image display unit 20 thatcauses the user to visually recognize a virtual image in a state inwhich the image display unit 20 is mounted on the head of the user and acontroller 10 that controls the image display unit 20.

The image display unit 20 is a mounted member mounted on the head of theuser. In this embodiment, the image display unit 20 has an eyeglassshape. The image display unit 20 includes ear hooking sections 21, aright display driving unit 22, a left display driving unit 24, anilluminance sensor 25, a right optical panel 26, and a left opticalpanel 28. The ear hooking sections 21 are members provided to transverseon the ears of the user from the ends of the right display driving unit22 and the left display driving unit 24 and function as temples. Theright optical panel 26 and the left optical panel 28 are arranged to berespectively located before the right and left eyes of the user in astate in which the user wears the image display unit 20. The rightdisplay driving unit 22 is arranged in a connecting place of the earhooking section 21 for the right ear and the right optical panel 26. Theleft display driving unit 24 is arranged in a connecting place of theear hooking section 21 for the left ear and the left optical panel 28.In the following explanation, the right display driving unit 22 and theleft display driving unit 24 are collectively referred to simply as“display driving unit”. The right optical panel 26 and the left opticalpanel 28 are collectively referred to simply as “optical panel”. Theilluminance sensor 25 functioning as the illuminance acquiring unit is asensor for acquiring ambient brightness (illuminance).

The display driving unit includes an LCD (Liquid Crystal Display), aprojection optical system, and the like, which are not shown in thefigure. Details are explained later. The optical panel includes a lightguide plate and a light modulating plate, which are not shown in thefigure. The light guide plate is formed of a light transmissive resinmaterial or the like and emits image light, which is captured from thedisplay driving unit, to the eyes of the user. The light modulatingplate is an optical device of a thin plate shape and is arranged tocover the front side (a side opposite to the side of the eyes of theuser) of the light guide plate. The light modulating plate protects thelight guide plate, suppresses, for example, damage and adhesion ofstains to the light guide plate, and adjusts the light transmittance ofthe light modulating plate. Consequently, the light modulating plate canadjust an amount of external light entering the eyes of the user andadjust easiness of visual recognition of a virtual image. The lightmodulating plate can be omitted. The image display unit 20 furtherincludes a right earphone 32 for the right ear and a left earphone 34for the left ear. The right earphone 32 and the left earphone 34 arerespectively worn on the right ear and the left ear when the user wearsthe image display unit 20.

The image display unit 20 further includes a connecting unit 40 forconnecting the image display unit 20 to a controller 10. The connectingunit 40 includes a main body cord 48 connected to the controller 10, aright cord 42 and a left cord 44, which are two cords branching from themain body cord 48, and a coupling member 46 provided at a branch point.The right cord 42 is connected to the right display driving unit 22. Theleft cord 44 is connected to the left display driving unit 24. The imagedisplay unit 20 and the controller 10 perform transmission of varioussignals via the connecting unit 40. Connectors (not shown) that fit witheach other are respectively provided at an end on the opposite side ofthe coupling member 46 in the main body cord 48 and the controller 10.The controller 10 and the image display unit 20 are connected anddisconnected by fitting the connector of the main body cord 48 and theconnector of the controller 10 and releasing the fitting. As the rightcord 42, the left cord 44, and the main body cord 48, for example, ametal cable and an optical fiber can be adopted.

The controller 10 is a device for operating the head mounted display HM.The controller 10 includes a lighting unit 12, a touch pad 14, a crosskey 16, and a power switch 18. The lighting unit 12 notifies anoperation state of the head mounted display HM (e.g., an ON or OFF stateof the power supply) with a light emission state of the lighting unit12. As the lighting unit 12, for example, an LED (Light Emitting Diode)can be used. The touch pad 14 detects finger operation by the user on anoperation surface of the touch pad 14 and outputs a signal correspondingto detection content. The cross key 16 detects pressing operation ofkeys corresponding to up, down, left, and right directions and outputs asignal corresponding to detection content. The power switch 18 detectsslide operation of the switch to switch a power-on state of the headmounted display HM.

FIG. 2 is a block diagram functionally showing the configuration of thehead mounted display HM. The controller 10 includes an input-informationacquiring unit 110, a storing unit 120, a power supply 130, a CPU 140,and an interface 180. These units are connected to one another by anot-shown bus. The input-information acquiring unit 110 includes afunction of acquiring a signal corresponding to an operation input bythe user (e.g., an operation input to a touch pad 14, the cross key 16,or the power switch 18). The storing unit 120 is a storing unitincluding a ROM, a RAM, a DRAM, and a hard disk, which are not shown inthe figure. Setting information CI is stored in the storing unit 120(details are explained later). The power supply 130 supplies electricpower to the units of the head mounted display HM. As the power supply130, for example, a secondary battery can be used.

The CPU 140 executes a computer program installed in advance to therebyprovide a function of an operating system (OS) 150. The CPU 140 expandsfirmware or a computer program stored in the ROM or the hard disk on theRAM and executes the firmware or the computer program to therebyfunction as an image processing unit 160 (details are explained later),a sound processing unit 170 (details are explained later), and a displaycontrol unit 190 (details are explained later).

The interface 180 is an interface for connecting various externalapparatuses OA (e.g., a personal computer PC, a cellular phone terminal,and a game terminal), which are supply sources of contents, to thecontroller 10. As the interface 180, the controller 10 can include, forexample, a USB interface, a micro USB interface, an interface for memorycard, or a wireless LAN interface. Contents mean information contentsincluding an image (a still image or a moving image) and sound. Theimage processing unit 160 generates a vertical synchronization signalVSync, a horizontal synchronization signal HSync, and image data Data onthe basis of contents input via the interface 180 and supplies thesesignals to the image display unit 20 via the connecting unit 40.Specifically, the image processing unit 160 acquires an image signalincluded in the contents. For example, in the case of a moving image,the acquired image signal is, in general, an analog signal includingthirty frame images per second. The image processing unit 160 separatessynchronization signals such as the vertical synchronization signalVSync and the horizontal synchronization signal HSync from the acquiredimage signal. The image processing unit 160 converts the analog imagesignal, from which the synchronization signals are separated, into adigital image signal using a not-shown A/D conversion circuit or thelike. Thereafter, the image processing unit 160 stores, frame by frame,the digital image signal after the conversion in the DRAM in the storingunit 120 as image data Data (RGB data) of a target image. The imageprocessing unit 160 outputs the image data Data of the target image asimage data for right eye and image data for left eye. The imageprocessing unit 160 may execute, on the image data, image processingsuch as resolution conversion processing, various kinds of color tonecorrection processing such as adjustment of luminance and chroma, andkeystone correction processing according to necessity.

The display control unit 190 generates control signals for controllingthe right display driving unit 22 and the left display driving unit 24and supplies the control signals to the image display unit 20 via theconnecting unit 40 to thereby control an image display state in theimage display unit 20. Specifically, the display control unit 190separately controls, according to the control signals,effectiveness/ineffectiveness of driving of a right LCD 241 by a rightLCD-control unit 211, effectiveness/ineffectiveness of driving of aright backlight 221 by a right-backlight control unit 201,effectiveness/ineffectiveness of driving of a left LCD 242 by a left-LCDcontrol unit 212, and effectiveness/ineffectiveness of driving of a leftbacklight 222 by a left-backlight control unit 202 to thereby controlpresence or absence of generation and emission of image lights by eachof the right display driving unit 22 and the left display driving unit24. Details are explained later.

The sound processing unit 170 acquires a sound signal included in thecontents, amplifies the acquired sound signal, and supplies the soundsignal to the right earphone 32 and the left earphone 34 of the imagedisplay unit 20 via the connecting unit 40.

The image display unit 20 includes the right display driving unit 22,the left display driving unit 24, a right light guide plate 261functioning as the right optical panel 26, a left light guide plate 262functioning as the left optical panel 28, the illuminance sensor 25, theright earphone 32, and the left earphone 34. The right display drivingunit 22 includes the right-backlight (BL) control unit 201 and theright-backlight (BL) 221 functioning as a light source, the rightLCD-control unit 211 and the right LCD 241 functioning as a displaydevice, a right temperature detecting unit 231 functioning as thetemperature detecting unit for right eye, and a right projection opticalsystem 251. The left display driving unit 24 includes the left-backlight(BL) control unit 202 and the left-backlight (BL) 222 functioning as alight source, the left-LCD control unit 212 and the left LCD 242functioning as a display device, a left temperature detecting unit 232functioning as the temperature detecting unit for left eye, and a leftprojection optical system 252. The right display driving unit 22 and theleft display driving unit 24 form a pair. The units of the left displaydriving unit 24 have configurations and perform operations same as thoseof the units of the right display driving unit 22 explained below.Therefore, detailed explanation of the units of the left display drivingunit 24 is omitted.

The right-backlight control unit 201 includes a function of driving theright backlight 221 on the basis of a control signal input via theconnecting unit 40. The right backlight 221 is, for example, a lightemitting member such as an LED. The right LCD-control unit 211 has afunction of driving the right LCD 241 on the basis of the verticalsynchronization signal VSync, the horizontal synchronization signalHSync, and the image data for right eye input via the connecting unit40. The right LCD 241 is a transmissive liquid crystal panel in whichplural pixels are arranged in a matrix shape. The right LCD 241 has afunction of driving liquid crystals corresponding to the positions ofthe pixels arranged in the matrix shape to thereby change thetransmittance of light transmitted through the right LCD 241 to modulateillumination light irradiated from the right backlight 221 intoeffective image light representing an image. The right-backlight controlunit 201, the right LCD-control unit 211, the right backlight 221, andthe right LCD 241 are generally referred to as “image-light generatingunit for right eye”. Similarly, the left-backlight control unit 202, theleft-LCD control unit 212, the left backlight 222, and the left LCD 242are generally referred to as “image-light generating unit for left eye”.In this embodiment, the backlight system is adopted. However, imagelight may be emitted using a front light system or a reflection system.

The right projection optical system 251 includes a collimate lens thatconverts image light emitted from the right LCD 241 into light beams ina parallel state. The right light guide plate 261 functioning as theright optical panel 26 guides the image light output from the rightprojection optical system 251 to the right eye of the user whilereflecting the image light along a predetermined optical path. The rightprojection optical system 251 and the right light guide plate 261 aregenerally referred to as “light guide unit”.

The right temperature detecting unit 231 is attached to an end of theright LCD 241 and includes a function of detecting the temperature ofthe right LCD 241. The right temperature detecting unit 231 includes,for example, a thermistor, a temperature sensor IC, and a fuse. Theright temperature detecting unit 231 may be configured as a non-contacttemperature sensor besides a contact temperature sensor.

FIG. 3 is an explanatory diagram showing an example of a virtual imagerecognized by the user. The image lights guided to the eyes of the userof the head mounted display HM form images on the retinas of the user asexplained above, whereby the user can visually recognize a virtualimage. As shown in FIG. 3, a virtual image VI is displayed in a visualfield VR of the user of the head mounted display HM. In the visual fieldVR of the user except a portion where the virtual image VI is displayed,the user can see an external scene SC through the right optical panel 26and the left optical panel 28. In the head mounted display HM in thisembodiment, in the portion where the virtual image VI is displayed inthe visual field VR of the user, the user can also see the externalscene SC in the background of the virtual image VI.

A-2. State Transition of the Head-Mounted Display Device

FIG. 4 is a state transition diagram showing states that the headmounted display HM could take. The head mounted display HM in thisembodiment can take a normal state SN and a power saving state SE. Inthe normal state SN, generation and emission of image light areperformed by both the image-light generating unit for right eye and theimage-light generating unit for left eye of the head mounted display HM.Therefore, in the normal state SN, a virtual image is displayed beforethe left and right eyes of the user. On the other hand, in the powersaving state SE, the generation and the emission of image light areperformed by one of the image-light generating unit for right eye andthe image-light generating unit for left eye of the head mounted displayHM. Therefore, in the power saving state SE, a virtual image isdisplayed before the left or right eye of the user.

When the head mounted display HM is in the normal state SN, the displaycontrol unit 190 monitors whether a power saving start condition issatisfied. After the power saving start condition is satisfied, thedisplay control unit 190 transitions the head mounted display HM to thepower saving state SE. When the head mounted display HM is in the powersaving state SE, the display control unit 190 monitors whether a powersaving stop condition is satisfied. After the power saving stopcondition is satisfied, the display control unit 190 transitions thehead mounted display HM to the normal state SN. A state that the headmounted display HM takes first when started (an initial state) may beeither the normal state SN or the power saving state SE.

A-2-1. Power Saving Start Condition

The power saving start condition can be arbitrarily set. For example,one or plural conditions can be selected out of conditions (a1) to (a7)listed below.

(a1) Content is a still image. The still image means an image having amain purpose of displaying information such as an initial screen of anOS, a screen of document creation software or mail software started onthe OS, or a play list display screen for music. The display controlunit 190 can determine, according to the type of an application startedon the OS, whether the content is a still image. If the condition (a1)is selected as the power saving start condition, the head mounteddisplay HM can take the power saving state SE according to the type of atarget image. Therefore, it is possible to realize low power consumptionaccording to the type of the target image. When the content is a stillimage, even in the power saving state SE for displaying a virtual imagebefore one eye of the user, the user can easily recognize the virtualimage displayed in a visual field area.(a2) The remaining power of the power supply 130 (the secondary battery)is equal to or smaller than predetermined remaining power. Thepredetermined remaining power can be arbitrarily set and is stored inthe setting information CI in the storing unit 120. If the condition(a2) is selected as the power saving start condition, the head mounteddisplay HM can take the power saving state SE when the remaining powerof the secondary battery runs short. Therefore, it is possible torealize low power consumption when the remaining power of the secondarybattery runs short. As a result, when the remaining power of the batteryruns short in the head mounted display HM that can be battery-driven, itis possible to increase an operating time of the battery.(a3) Illuminance acquired by the illuminance sensor 25 is equal to orlower than predetermined illuminance. The predetermined illuminance canbe arbitrarily set and is stored in the setting information CI in thestoring unit 120. If the condition (a3) is selected as the power savingstart condition, the head mounted display HM can take the power savingstate SE when the ambient brightness is equal to or lower than thepredetermined illuminance, i.e., when the environment is dark.Therefore, it is possible to realize low power consumption when theenvironment is dark. When the environment is dark, even in the powersaving state SE for displaying a virtual image before one eye of theuser, the user can easily recognize the virtual image displayed in thevisual field area.(a4) One of the temperature of the right LCD 241 detected by the righttemperature detecting unit 231 and the temperature of the left LCD 242detected by the left temperature detecting unit 232 is equal to orhigher than predetermined temperature. The predetermined temperature canbe arbitrarily set and is stored in the setting information CI in thestoring unit 120. If the condition (a4) is selected as the power savingstart condition, the head mounted display HM can take the power savingstate SE when the temperature of the image-light generating unit forright eye or the image-light generating unit for left eye is equal to orhigher than predetermined temperature, i.e., when the temperature of theleft or right image-light generating units rises. Therefore, it ispossible to realize low power consumption when the temperature of theleft or right image-light generating units is high. It is desirable tosuppress the rise in the temperature of the image-light generating unitbecause the rise in the temperature leads to a failure of the LCD.Consequently, since the low power consumption is realized when thetemperature of the left or right image-light generating unit is high, itis possible to suppress a further rise in the temperature of theimage-light generating unit.(a5) Startup of an application designated in advance in the OS isdetected. As the designation of the application, for example,designation by the user is possible. Content of the designation isstored in the setting information CI in the storing unit 120. If thecondition (a5) is selected as the power saving start condition, the headmounted display HM can take the power saving state SE according to thestartup of the application designated in advance.(a6) A power saving request is acquired from the outside. Specifically,the display control unit 190 acquires a request for selection of powersaving via the touch pad 14 or the cross key 16 provided in thecontroller 10. If the condition (a6) is selected as the power savingstart condition, the head mounted display HM can take the power savingstate SE according to operation from the touch pad 14 or the cross key16.(a7) A state in which operation for the head mounted display HM (e.g.,operation for the touch pad 14 and the cross key 16) is not detectedcontinues for a predetermined time. The predetermined time can bearbitrarily set and is stored in the setting information CI in thestoring unit 120. If the condition (a7) is selected as the power savingstart condition, the head mounted display HM can take the power savingstate SE when operation for the head mounted display HM is not performedfor a long time.

(A-2-2) Power Saving Stop Condition

The power saving stop condition can be arbitrarily set. For example, oneor plural conditions can be selected out of conditions listed below. Inthe following explanation, when a number affixed to the end of areference number of the power saving stop condition is the same as anumber affixed to a reference number of the power saving startcondition, the power saving stop condition corresponds to the powersaving start condition. The power saving stop condition is desirably acondition corresponding to the power saving start condition.Specifically, when the power saving start condition is the condition(a1), the power saving stop condition is desirably a condition (b1).

(b1) Content is a moving image. The moving image means an image having amain purpose of displaying a video such as a screen for displaying avideo and a game screen. It is possible to determine, according to thetype of an application started on the OS, whether the content is amoving image. When a displayed image is a moving image that constantlychanges, the head mounted display HM takes the normal state SN, wherebya virtual image is displayed before the left and right eyes of the user.If the power saving stop condition (b1) and the power saving startcondition (a1) are used as a set, it is possible to secure visibility ofthe user while realizing low power consumption in the head mounteddisplay HM.(b2) The remaining power of the power supply 130 (the secondary battery)exceeds the predetermined remaining power. If the power saving stopcondition (b2) and the power saving start condition (a2) are used as aset, the head mounted display HM transitions to the normal state SN whenthe battery remaining power of the head mounted display HM exceeds thepredetermined remaining power (i.e., charging is performed). A virtualimage is displayed before the left and right eyes of the user. As aresult, it is possible to improve visibility of the user while realizinglow power consumption.(b3) Illuminance acquired by the illuminance sensor 25 exceeds thepredetermined illuminance. If the power saving stop condition (b3) andthe power saving start condition (a3) are used as a set, the headmounted display HM transitions to the normal state SN when theenvironment is bright and the user can less easily recognize a virtualimage. A virtual image is displayed before the left and right eyes ofthe user. As a result, it is possible to secure visibility of the userwhile realizing low power consumption.(b4) Both the temperature of the right LCD 241 detected by the righttemperature detecting unit 231 and the temperature of the left LCD 242detected by the left temperature detecting unit 232 are lower than thepredetermined temperature. If the power saving stop condition (b4) andthe power saving start condition (a4) are used as a set, the headmounted display HM transitions to the normal state SN when thetemperatures of the left and right image-light generating units fall. Avirtual image is displayed before the left and right eyes of the user.As a result, it is possible to secure visibility of the user whilerealizing low power consumption.(b5) The end of an application set in advance in the OS is detected. Ifthe power saving stop condition (b5) and the power saving startcondition (a5) are used as a set, the head mounted display HM can switchthe normal state SN and the power saving state SE according to thestartup and the end of a specific application designated in advance bythe user or the like.(b6) A power saving release request is received from the outside.Specifically, the display control unit 190 acquires a request forrelease of the power saving state via the touch pad 14 or the cross key16 provided in the controller 10. If the power saving stop condition(b6) and the power saving start condition (a6) are used as a set, thehead mounted display HM can switch the normal state SN and the powersaving state SE according to a request from the outside.(b7) Operation for the head mounted display HM (e.g., operation for thetouch pad 14 and the cross key 16) is detected. If the power saving stopcondition (b7) and the power saving start condition (a7) are used as aset, it is possible to realize lower power consumption in the headmounted display HM.

FIG. 5 is a flowchart for explaining a procedure of processing performedwhen the head mounted display HM transitions to the normal state SN. Thedisplay control unit 190 reproduces left and right images (step S102).Specifically, the display control unit 190 transmits control signalsindicating “effective” respectively to the right-LCD control unit 211and the left-LCD control unit 212. The right-LCD control unit 211 thatreceives the control signal indicating “effective” drives the right LCD241 and generates an image on the basis of image data for right eyeinput to the right-LCD control unit 211. The same applies to theleft-LCD control unit 212. Subsequently, the display control unit 190turns on the left and right backlights (step S104). Specifically, thedisplay control unit 190 transmits control signals indicating“effective” respectively to the right-backlight control unit 201 and theleft-backlight control unit 202. The right-backlight control unit 201that receives the control signal indicating “effective” turns on theright backlight 221 to irradiate illumination light on the imagegenerated by the right LCD 241 and emits image light representing theimage. The same applies to the left-backlight control unit 202.

FIGS. 6A and 6B are explanatory diagrams showing a state in which imagelight is emitted through the processing shown in FIG. 5. FIG. 6A shows astate in which image light PL is emitted by irradiation of illuminationlight IL in the image-light generating unit for right eye. FIG. 6B showsa state in which the image light PL is emitted by irradiation of theillumination light IL in the image-light generating unit for left eye.As a result, the generation and the emission of image light areperformed by both the image-light generating unit for right eye and theimage-light generating unit for left eye of the head mounted display HM.Therefore, in the normal state SN, a virtual image is displayed beforethe left and right eyes of the user. In the normal state SN, theirradiation of the illumination light (step S104) is performed after thegeneration of the image light (step S102). Therefore, it is possible tosuppress flickering in display of a virtual image and smoothly performdisplay of the virtual image.

FIG. 7 is a flowchart for explaining a procedure of processing performedwhen the head mounted display HM transitions to the power saving stateSE. The display control unit 190 turns off the right backlight 221 (stepS202). Specifically, the display control unit 190 transmits a controlsignal indicating “ineffective” to the right-backlight control unit 201and transmits a control signal indicating “effective” to theleft-backlight control unit 202. The right-backlight control unit 201that receives the control signal indicating “ineffective” turns offillumination light of the right backlight 221. Therefore, an imagegenerated by the right LCD 241 is not emitted as image light. On theother hand, the left-backlight control unit 202 that receives thecontrol signal indicating “effective” keeps illumination light of theleft backlight 222 on. Therefore, an image generated by the left LCD 242is emitted as image light.

FIGS. 8A and 8B are explanatory diagrams showing states of theimage-light generating units at a point when the processing in step S202in FIG. 7 ends. As shown in FIG. 8A, in the image-light generating unitfor right eye, the illumination light is turned off, whereby theemission of the image light is stopped. On the other hand, as shown inFIG. 8B, in the image-light generating unit for left eye, the emissionof the image light PL is continued by the irradiation of theillumination light IL.

Subsequently, in step S204 in FIG. 7, the display control unit 190 stopsreproduction of a right image. Specifically, the display control unit190 transmits a control signal indicating “ineffective” to the right-LCDcontrol unit 211 and transmits a control signal indicating “effective”to the left-LCD control unit 212. The right-LCD control unit 211 thatreceives the control signal indicating “ineffective” stops driving ofthe right LCD 241. Consequently, the generation of an image by the LCDis stopped. On the other hand, the left-LCD control unit 212 thatreceives the control signal indicating “effective” continues driving ofthe left LCD 242.

As a result, the generation and the emission of image light by theimage-light generating unit for right eye of the head mounted display HMare stopped. Only the image-light generating unit for left eye performsthe generation and the emission of image light. Therefore, in the powersaving state SE, a virtual image is displayed before the left eye of theuser. In the power saving state SE, the stop of the image light (stepS204) is performed after the stop of the irradiation of the illuminationlight (step S202). Therefore, it is possible to suppress flickeringduring the stop of the virtual image display and smoothly extinguish thevirtual image.

In this embodiment, in the power saving state SE, a virtual image isdisplayed before the left eye of the user, i.e., the generation and theemission of image light by the image-light generating unit for right eyeare stopped. However, the display of a virtual image and the stop of thegeneration and the emission of image light may be reversed. In otherwords, the generation and the emission of image light by the image-lightgenerating unit for left eye may be stopped. In the power saving stateSE, the user can designate which of the image-light generating unit forright eye and the image-light generating unit for left eye is stopped.Specifically, the user selects one of the image-light generating unitfor right eye and the image-light generating unit for left eye, thegeneration and the emission of image light by which are stopped, byoperating the touch pad 14 or the cross key 16 provided in thecontroller 10 functioning as the selection receiving unit.

FIGS. 9A to 9C are explanatory diagrams showing an example of statetransition of the head mounted display HM. In the example shown in FIGS.9A to 9C, the initial state of the head mounted display HM is the powersaving state SE, the condition (a1) is adopted as the power saving startcondition, and the condition (b1) is adopted as the power saving stopcondition.

FIG. 9A shows states of the right LCD 241 and the left LCD 242 at timet1 when the head mounted display HM is started. Since the initial stateof the head mounted display HM is the power saving state SE, during thestartup of the head mounted display HM, the display control unit 190executes the processing performed when the head mounted display HMtransitions to the power saving state SE (FIG. 7). As a result, thegeneration and the emission of image light are performed by only theimage-light generating unit for left eye (the left LCD 242) of the headmounted display HM. A virtual image based on image light shown in FIG.9A is displayed before the left eye of the user.

FIG. 9B shows states of the right LCD 241 and the left LCD 242 at timet2 when reproduction of a moving image is started in the head mounteddisplay HM. When the display control unit 190 detects startup of anapplication for reproducing a moving image (a video) (a moving imageviewer VW), the display control unit 190 determines that the powersaving stop condition (b1) is satisfied and executes the processingperformed when the head mounted display HM transitions to the normalstate SN (FIG. 5). As a result, the generation and the emission of imagelight are performed by both the image-light generating unit for righteye (the right LCD 241) and the image-light generating unit for left eye(the left LCD 242) of the head mounted display HM. A virtual image basedon image light shown in FIG. 9B is displayed before the left and righteyes of the user.

FIG. 9C shows states of the right LCD 241 and the left LCD 242 at timet3 when the reproduction of the moving image ends in the head mounteddisplay HM. When the display control unit 190 detects the end of themoving image viewer VW and detects that display of the head mounteddisplay HM changes to the initial screen display of the OS, the displaycontrol unit 190 determines that the power saving start condition (a1)is satisfied and executes the processing performed when the head mounteddisplay HM transitions to the power saving state SE (FIG. 7). As aresult, the generation and the emission of image light are performed byonly the image-light generating unit for left eye (the left LCD 242) ofthe head mounted display HM. A virtual image based on image light shownin FIG. 9C is displayed before the left eye of the user.

As explained above, in the first embodiment, the display control unit190 can control, with a control signal, the generation and the emissionof image light by each of the image-light generating unit for right eyeand the image-light generating unit for left eye. Therefore, the displaycontrol unit 190 can realize the normal state SN in which the generationand the emission of image light are performed by both the image-lightgenerating unit for right eye and the image-light generating unit forleft eye and the power saving state SE in which the generation and theemission of image light are performed by one of the image-lightgenerating unit for right eye and the image-light generating unit forleft eye. In the power saving state SE, a virtual image is displayedbefore one eye (the left or right eye) of the user. Even the virtualimage displayed before one eye can be recognized as one virtual image VIdisplayed in the visual field of the user as in FIG. 3 if the user isconscious of the virtual image. Electric power for driving the LCDsaccounts for about ⅓ of electric power consumed by the head mounteddisplay HM as a whole. Therefore, in the power saving state SE in whichonly one of the left and right LCDs has to be driven, it is possible tosuppress power consumption of the head mounted display HM as a wholecompared with the normal state SN. As a result, in the head mounteddisplay HM, it is possible to realize low power consumption withoutdeteriorating the image quality of the virtual image that the userrecognizes.

B. Second Embodiment

In a second embodiment of the invention, in the power saving state SE, aconfiguration for causing the image-light generating unit for right eyeand the image-light generating unit for left eye to alternately displaya virtual image is explained. In the following explanation, onlycomponents that have configurations and perform operations differentfrom those in the first embodiment are explained. In the figures,components same as those in the first embodiment are denoted byreference numerals and signs same as those in the first embodimentexplained above and detailed explanation of the components is omitted.

B-1. Configuration of the Head-Mounted Display Device

The configuration of the head mounted display HM in the secondembodiment is the same as the configuration in the first embodimentexplained with reference to FIGS. 1 to 3.

B-2. State Transition of the Head-Mounted Display Device

FIG. 10 is a state transition diagram showing states that the headmounted display HM in the second embodiment could take. A differencefrom the state transition in the first embodiment shown in FIG. 4 isonly that in the power saving state SE, the head mounted display HMtakes a first state SE1 and a second state SE2. The other operations arethe same as those in the first embodiment. In the first state SE1,generation and emission of image light are performed by the image-lightgenerating unit for left eye of the head mounted display HM. Generationand emission of image light are stopped by the image-light generatingunit for right eye of the head mounted display HM. Therefore, in thefirst state SE1, a virtual image is displayed before the left eye of auser. In the second state SE2, generation and emission of image lightare performed by the image-light generating unit for right eye of thehead mounted display HM. Generation and emission of image light arestopped in the image-light generating unit for left eye of the headmounted display HM. Therefore, in the second state SE2, a virtual imageis displayed before the right eye of the user.

When the head mounted display HM is in the power saving state SE, thedisplay control unit 190 monitors whether a switching condition issatisfied. After the switching condition is satisfied, when the headmounted display HM is in the first state SE1, the display control unit190 transitions the head mounted display HM to the second state SE2.When the head mounted display HM is in the second state SE2, the displaycontrol unit 190 transitions the head mounted display HM to the firststate SE1. A state that the head mounted display HM takes first whentransitioning to the power saving state SE may be either the first stateSE1 or the second state SE2.

B-2-1. Switching Condition

The switching condition can be arbitrarily set. For example, one orplural conditions may be selected out of conditions listed below.

(c1) After state transition, a fixed time elapses. The fixed time can bearbitrarily set. For example, the fixed time may be several minutes ormay be, for example, a time until thirty frames are displayed. If thecondition (c1) is selected as the switching condition, it is possible toequally switch the image-light generating unit for right eye and theimage-light generating unit for left eye.(c2) A difference between the temperature of the right LCD 241 detectedby the right temperature detecting unit 231 and the temperature of theleft LCD 242 detected by the left temperature detecting unit 232 isequal to or larger than a predetermined temperature difference. Thepredetermined temperature difference can be arbitrarily set and isstored in the setting information CI in the storing unit 120. If thecondition (c2) is selected as the switching condition, it is possible toswitch the image-light generating unit for right eye and the image-lightgenerating unit for left eye to perform the generation and the emissionof image light using the image-light generating unit on a side where thegeneration and the emission of image light are stopped (i.e., a sidewhere the temperature of the LCD is low). As a result, the first stateSE1 and the second state SE2 can be switched according to thetemperatures of the LCDs. Therefore, it is possible to suppress thetemperature of only one image-light generating unit from rising.

A procedure of processing performed when the head mounted display HMtransitions to the first state SE1 is the same as the procedure shown inFIG. 7. As a result, the generation and the emission of image light bythe image-light generating unit for right eye of the head mounteddisplay HM are stopped and only the image-light generating unit for lefteye performs the generation and the emission of image light. Therefore,in the first state SE1, a virtual image is displayed before the left eyeof the user.

FIG. 11 is a flowchart for explaining a procedure of processingperformed when the head mounted display HM in the second embodimenttransitions to the second state SE2. The display control unit 190 turnsoff the left backlight 222 (step S302). Specifically, the displaycontrol unit 190 transmits a control signal indicating “effective” tothe right-backlight control unit 201 and transmits a control signalindicating “ineffective” to the left-backlight control unit 202. Theright-backlight control unit 201 that receives the control signalindicating “effective” keeps illumination light of the right backlight221 on. Therefore, an image generated by the right LCD 241 is emitted asimage light. On the other hand, the left-backlight control unit 202 thatreceives the control signal indicating “ineffective” turns offillumination light of the left backlight 222. Therefore, an imagegenerated by the left LCD 242 is not emitted as image light. FIGS. 12Aand 12B are explanatory diagrams showing states of the image-lightgenerating units at a point when the processing in step S302 in FIG. 11ends.

Subsequently, the display control unit 190 stops the reproduction of theleft image (step S304). Specifically, the display control unit 190transmits a control signal indicating “effective” to the right-LCDcontrol unit 211 and transmits a control signal indicating “ineffective”to the left-LCD control unit 212. The right-LCD control unit 211 thatreceives the control signal indicating “effective” continues driving ofthe right LCD 241. On the other hand, the left-LCD control unit 212 thatreceives the control signal indicating “ineffective” stops driving ofthe left LCD 242. Consequently the generation of the image by the leftLCD 242 is stopped. As a result, the generation and the emission ofimage light by the image-light generating unit for left eye of the headmounted display HM are stopped. Only the image-light generating unit forright eye performs the generation and the emission of image light.Therefore, in the second state SE2, a virtual image is displayed beforethe right eye of the user. Step S204 of the processing performed whenthe head mounted display HM transitions to the first state SE1 (FIG. 7)and step S304 of the processing performed when the head mounted displayHM transitions to the second state SE2 can be omitted. Then, presence orabsence of display of a virtual image can be switched by only turning onand off the backlights. Therefore, it is possible to quickly switch thefirst state SE1 and the second state SE2.

FIGS. 13A and 13B are explanatory diagrams showing an example of statetransition of the head mounted display HM in the second embodiment. Inthe example shown in FIGS. 13A and 13B, a state that the head mounteddisplay HM takes first when transitioning to the power saving state SEis the first state SE1 and the condition (c1) is adopted as theswitching condition.

FIG. 13A shows states of the right LCD 241 and the left LCD 242 at timet1 when the head mounted display HM transitions to the power savingstate SE. When the head mounted display HM transitions to the powersaving state SE, the display control unit 190 executes the processingperformed when the head mounted display HM transitions to the firststate SE1 (FIG. 7). As a result, the generation and the emission ofimage light are performed by only the image-light generating unit forleft eye (the left LCD 242) of the head mounted display HM. A virtualimage based on image light shown in FIG. 13A is displayed before theleft eye of the user.

FIG. 13B shows states of the right LCD 241 and the left LCD 242 at timet2 after the elapse of a fixed time from time t1. After the head mounteddisplay HM transitions to the first state SE1, when the fixed timeelapses, the display control unit 190 determines that the switchingcondition (c1) is satisfied and executes the processing performed whenthe head mounted display HM transitions to the second state SE2 (FIG.11). As a result, the generation and the emission of image light areperformed by only the image-light generating unit for right eye (theright LCD 241) of the head mounted display HM. A virtual image based onimage light shown in FIG. 13B is displayed before the right eye of theuser.

As explained above, in the second embodiment, the display control unit190 alternately switches, triggered by the satisfaction of the switchingcondition, the first state SE1 for causing one (the image-lightgenerating unit for right eye) of the image-light generating unit forright eye and the image-light generating unit for left eye to stop thegeneration and the emission of image light and causing the other (theimage-light generating unit for left eye) to execute the generation andthe emission of image light and the second state SE2 for causing one(the image-light generating unit for right eye) to execute thegeneration and the emission of image light and causing the other (theimage-light generating unit for left eye) to stop the generation and theemission of image light. Therefore, as in the first embodiment, in thehead mounted display HM, it is possible to realize low power consumptionwithout deteriorating the image quality of a virtual image recognized bythe user. In the second embodiment, the display control unit 190 causesthe image-light generating unit for right eye and the image-lightgenerating unit for left eye to alternately display a virtual image. Inthis way, compared with continuous use of only one image-lightgenerating unit, it is possible to suppress a rise in temperature,deterioration, and the like involved in continuous use of the LCD.

C. Third Embodiment

In a third embodiment of the invention, a configuration for switching,in switching the first state SE1 and the second state SE2, the firststate SE1 and the second state SE2 through a third state for causingboth the image-light generating unit for right eye and the image-lightgenerating unit for left eye to display a virtual image is explained. Inthe figures, components same as those in the second embodiment aredenoted by reference numerals and signs same as those in the secondembodiment explained above and detailed explanation of the components isomitted.

C-1. Configuration of a Head-Mounted Display Device

The configuration of the head mounted display HM in the third embodimentis the same as the configuration in the first embodiment explained withreference to FIGS. 1 to 3.

C-2. State Transition of the Head-Mounted Display Device

FIG. 14 is a state transition diagram showing states that the headmounted display HM in the third embodiment could take. A difference fromthe state transition in the second embodiment shown in FIG. 10 is onlythat the head mounted display HM further includes a third state SE3between the first state SE1 and the second state SE2. The otheroperations are the same as those in the second embodiment. In the thirdstate SE3, generation and emission of image light are performed by boththe image-light generating unit for right eye and the image-lightgenerating unit for left eye of the head mounted display HM. When thehead mounted display HM is in the power saving state SE, the displaycontrol unit 190 monitors whether a switching condition is satisfied.After the switching condition is satisfied, when the head mounteddisplay HM is in the first state SE1, the display control unit 190transitions the head mounted display HM to the second state SE2 throughthe third state SE3. When the head mounted display HM is in the secondstate SE2, the display control unit 190 transitions the head mounteddisplay HM to the first state SE1 through the third state SE3. A timeduring which the head mounted display HM stays in the third state SE3can be set to an arbitrary time. However, the time is desirably set to ashort time (several seconds).

A procedure of processing performed when the head mounted display HMtransitions to the third state SE3 is the same as the procedure shown inFIG. 5. As a result, the generation and the emission of image light areperformed by both the image-light generating unit for right eye and theimage-light generating unit for left eye of the head mounted display HM.Therefore, in the third state SE3, a virtual image is displayed beforethe left and right eyes of a user.

FIGS. 15A to 15C are explanatory diagrams showing an example of statetransition of the head mounted display HM in the third embodiment. Adifference from the state transition in the second embodiment shown inFIGS. 13A and 13B is that, after the head mounted display HM transitionsto the first state SE1, when a fixed time elapses, the head mounteddisplay HM transitions to the second state SE2 shown in FIG. 15C throughthe third state SE3 shown in FIG. 15B.

As explained above, in the third embodiment, in switching the firststate SE1 and the second state SE2, the display control unit 190switches the first state SE1 and the second state SE2 through the thirdstate SE3 for causing both the image-light generating unit for right eyeand the image-light generating unit for left eye to perform thegeneration and the emission of image light. As a result, it is possibleto reduce a sense of discomfort that the user feels during the switchingof the first state SE1 and the second state SE2 and more naturallyperform the switching.

D. Modifications

The invention is not limited to the embodiments and can be carried outin various forms without departing from the spirit of the invention. Forexample, the functions realized by software may be realized by hardware.Besides, modifications explained below are possible.

D1. Modification 1

In the embodiments, the configuration of the head mounted display isexemplified. However, the configuration of the head mounted display canbe arbitrarily set without departing from the spirit of the invention.For example, addition, deletion, conversion, and the like of thecomponents can be performed.

For example, the configurations of the controller and the image displayunit shown in FIG. 1 can be arbitrarily changed. Specifically, forexample, the touch panel may be omitted from the controller and thecontroller may be operated only with the cross key. Other operationinterfaces such as an operation stick may be provided in the controller.Input devices such as a keyboard and a mouse can be connected to thecontroller. The controller may receive inputs from the keyboard and themouse. A communication unit employing Wi-Fi (wireless fidelity) may beprovided in the controller.

For example, the controller shown in FIG. 1 is connected to the imagedisplay unit via a wired signal transmission line. However, thecontroller and the image display unit may be connected via a wirelesssignal transmission line such as a wireless LAN, infrared communication,or Bluetooth (registered trademark).

For example, the head mounted display is the transmissive head mounteddisplay of a binocular type. However, the head mounted display may beconfigured as a non-transmissive head mounted display that blocks anexternal scene when the user wears the head mounted display. The headmounted display may be a head mounted display of a monocular type.

For example, the image-light generating unit for right eye is configuredusing the right-backlight control unit, the right-LCD control unit, theright backlight, and the right LCD. However, an organic EL (organicElectro-Luminescence) and an organic EL control unit may be used insteadof the right-backlight control unit, the right-LCD control unit, theright backlight, and the right LCD. In the case of the organic EL, sincedeterioration involved in a temperature rise is severer than thedeterioration of the LCD, the invention is particularly effective. Thesame applies to the image-light generating unit for left eye.

For example, the functional units such as the image processing unit, thedisplay control unit, and the sound processing unit are described asbeing realized by the CPU expanding the computer program stored in theROM or the hard disk on the RAM and executing the computer program.However, these functional units may be configured using an ASIC(Application Specific Integrated Circuit) designed to realize thefunctions.

For example, in the embodiments, the image display unit is the headmounted display worn like eyeglasses. However, the image display unitmay be a normal flat display device (a liquid crystal display device, aplasma display device, an organic EL display device, etc.) In this case,as in the head mounted display, the controller and the image displayunit may be connected via the wired signal transmission line or may beconnected via the wireless signal transmission line. In this way, thecontroller can be used as a remote controller of the normal flat displaydevice.

As the image display unit, an image display unit having another shapesuch as an image display unit worn like a cap may be adopted instead ofthe image display unit worn line eyeglasses. As the earphone, an earhooking type or a headband type may be adopted. The earphone may beomitted.

For example, in the embodiments, the secondary battery is used as thepower supply. However, the power supply is not limited to the secondarybattery. Various batteries can be used as the power supply. For example,a primary battery, a fuel cell, a solar battery, a thermal battery, andthe like may be used.

D2. Modification 2

In the embodiments, the image processing unit outputs the same imagedata as the image data for right eye and the image data for left eye.However, the image processing unit may be configured to be capable ofcausing the user to visually recognize a 3D virtual image by outputtingdifferent image data as the image data for right eye and the image datafor left eye.

D3. Modification 3

In the first embodiment, the examples of the power saving startcondition and the power saving stop condition are explained. However,the transition conditions explained in the first embodiment are onlyexamples. Various conditions can be adopted.

For example, when the head mounted display can cause the user tovisually recognize a 3D virtual image, the power saving start conditionmay be a condition that the head mounted display is in a mode fordisplaying a 3D virtual image. The power saving stop condition may be acondition that the head mounted display is in a mode for displaying a 2Dvirtual image.

D4. Modification 4

In the second embodiment, the example of the switching condition isexplained. However, the switching condition explained in the secondembodiment is only an example. Various conditions can be adopted.

D5. Modification 5

In the third embodiment, in the third state through which the firststate and the second state are switched, a virtual image is displayed byboth the image-light generating unit for right eye and the image-lightgenerating unit for left eye. However, the third state may be a statefor stopping the display of a virtual image in both the image-lightgenerating unit for right eye and the image-light generating unit forleft eye.

The entire disclosure of Japanese Patent Application Nos. 0.2011-026810,filed Feb. 10, 2011 and 2011-026809, filed Feb. 10, 2011 are expresslyincorporated by reference herein.

What is claimed is:
 1. A head-mounted display device for making a userrecognize a virtual image in a state in which the head-mounted displaydevice is mounted on a head of the user, the head-mounted display devicecomprising: an image-light generating unit for the right eye of the userto generate an image light from image data for right eye of the user andto emit the image light; an image-light generating unit for the left eyeof the user to generate the image light from image data for the left eyeof the user and to emit the image light; a display control unitconfigured to control an emission of each of the image lightrespectively generated by the image-light generating unit for the righteye of the user and the image-light generating unit for the left eye ofthe user; a temperature detecting unit for the right eye of the userthat detects a temperature of the image-light generating unit for theright eye of the user; and a temperature detecting unit for the left eyeof the user that detects a temperature of the image-light generatingunit for the left eye of the user, wherein the display control unitcontrols the head-mounted display device to change its operation state,according to a condition set in advance, to a power saving state,wherein in the power saving state, the display control unit transitionsthe image-light emission of the image-light generating units among afirst state in which only the image-light generating unit for the lefteye of the user emits image light, a second state in which only theimage-light generating unit for the right eye of the user emits imagelight, and a third state in which both the image-light generating unitsfor the left eye of the user and for the right eye of the user emitimage light, when a switching condition is satisfied, the displaycontrol unit is configured to transition the image-light emission of theimage-light generating units from the first state to the second statethrough the third state, when a first condition is selected, the displaycontrol unit is configured to transition the image-light emission of theimage-light generating units from equally between the first state andthe second state, and when a second condition is selected, the displaycontrol unit is configured to transition the image-light emission of theimage-light generating units from one of the first state and the secondstate to the other of the first state and the second state.
 2. Thehead-mounted display device according to claim 1, wherein the conditionset in advance is a condition that at least one of the temperaturedetected by the temperature detecting unit for the right eye of the userand the temperature detected by the temperature detecting unit for theleft eye of the user is equal to or higher than a predeterminedtemperature.
 3. The head-mounted display device according to claim 1,wherein the condition set in advance is a condition that a target imageused for display of the virtual image is a still image.
 4. Thehead-mounted display device according to claim 1, further comprising abattery that supplies electric power to the head-mounted display device,wherein the condition set in advance is a condition that a remainingpower of the battery is equal to or smaller than a predeterminedremaining power.
 5. The head-mounted display device according to claim1, further comprising an illuminance acquiring unit that acquires anilluminance indicating ambient brightness, wherein the condition set inadvance is a condition that the acquired illuminance is equal to orlower than a predetermined illuminance.
 6. The head-mounted displaydevice according to claim 1, wherein the condition set in advance is anyone of a condition that the head-mounted display device detects startupof an application designated in advance in an operating system installedin the head-mounted display device, a condition that the head-mounteddisplay device acquires a request from an outside, and a condition thatthe head-mounted display device detects that a state in which operationfor the head-mounted display device is not detected continues for apredetermined time.
 7. The head-mounted display device according toclaim 1, wherein when the second condition is selected and if thetemperature of the image-light generating unit for the left eye of theuser is lower than the temperature of the image-light generating unitfor the right eye of the user, the display control unit is configured totransition to the first state.
 8. The head-mounted display deviceaccording to claim 1, wherein when the second condition is selected andif the temperature of the image-light generating unit for the left eyeof the user is higher than the temperature of the image-light generatingunit for the right eye of the user, the display control unit isconfigured to transition to the second state.
 9. A head-mounted displaydevice for making a user recognize a virtual image in a state in whichthe head-mounted display device is mounted on a head of the user, thehead-mounted display device comprising: an image-light generating unitfor the right eye of the user to generate an image light from image datafor the right eye of the user and to emit the image light; animage-light generating unit for the left eye of the user to generate theimage light from image data for the left eye of the user and to emit theimage light; a display control unit configured to control an emission ofeach of the image light respectively generated by the image-lightgenerating unit for the right eye of the user and the image-lightgenerating unit for the left eye of the user; a temperature detectingunit for the right eye of the user that detects a temperature of theimage-light generating unit for the right eye of the user; and atemperature detecting unit for the left eye of the user that detects atemperature of the image-light generating unit for the left eye of theuser, wherein the display control unit controls the head-mounted displaydevice to change its operation state, according to conditions set inadvance, between a power saving state, and a normal state which makesboth of the image-light generating unit for the right eye of the userand the image-light generating unit for the left eye of the user executethe emission of the image light, wherein in the power saving state, thedisplay control unit transitions the image-light emission of theimage-light generating units among a first state in which only theimage-light generating unit for the left eye of the user emits imagelight, a second state in which only the image-light generating unit forthe right eye of the user emits image light, and a third state in whichboth the image-light generating units for the left eye of the user andfor the right eye of the user emit image light, the conditions set inadvance are a first condition that at least one of the temperaturedetected by the temperature detecting unit for the right eye of the userand the temperature detected by the temperature detecting unit for theleft eye of the user is equal to or higher than a predeterminedtemperature, the first condition causing the head-mounted display deviceto change its operation state to the power saving state, and a secondcondition that both of the temperature detected by the temperaturedetecting unit for the right eye of the user and the temperaturedetected by the temperature detecting unit for the left eye of the userare below the predetermined temperature, the second condition making thehead-mounted display device to change its operation state to the normalstate, and when a switching condition is satisfied, the display controlunit is configured to transition the image-light emission of theimage-light generating units from the first state to the second statethrough the third state, when a first condition is selected, the displaycontrol unit is configured to transition the image-light emission of theimage-light generating units from equally between the first state andthe second state, and when a second condition is selected, the displaycontrol unit is configured to transition the image-light emission of theimage-light generating units from one of the first state and the secondstate to the other of the first state and the second state.
 10. Thehead-mounted display device according to claim 9, further comprising animage processing unit that receives a source image which becomes thevirtual image and generates the image data for right eye of the user andthe image data for left eye of the user based on the source image. 11.The head-mounted display device according to claim 9, wherein the imagelight emitted by the image-light generating unit that executes theemission of the image light in the power saving state is a same size asan image light emitted in a non-power saving state.
 12. The head-mounteddisplay device according to claim 9, wherein the virtual image made inthe power saving state by one of the image-light generating unit for theright eye of the user and the image-light generating unit for the lefteye of the user display in the virtual field of the user is the same asthe virtual image displayed in the normal state.
 13. The head-mounteddisplay device according to claim 12, further comprising an imageprocessing unit that receives a source image which becomes the virtualimage and generates the image data for the right eye of the user and theimage data for the left eye of the user based on the source image. 14.The head-mounted display device according to claim 12, wherein the imagelight emitted by image-light generating unit that executes the emissionof the image light in the power saving state is a same size as an imagelight emitted in a non-power saving state.
 15. A head-mounted displaydevice for making a user recognize a virtual image in a state in whichthe head-mounted display device is mounted on a head of the user, thehead-mounted display device comprising: an image-light generating unitfor the right eye of the user to generate an image light from image datafor the right eye of the user and to emit the image light; animage-light generating unit for the left eye of the user to generate theimage light from image data for the left eye of the user and to emit theimage light; a display control unit configured to control an emission ofeach of the image light respectively generated by the image-lightgenerating unit for the right eye of the user and the image-lightgenerating unit for the left eye of the user; a temperature detectingunit for the right eye of the user that detects a temperature of theimage-light generating unit for the right eye of the user; and atemperature detecting unit for the left eye of the user that detects atemperature of the image-light generating unit for the left eye of theuser, wherein the display control unit controls the head-mounted displaydevice to change its operation state, according to a condition set inadvance, between a power saving state and a normal state which makesboth of the image-light generating unit for the right eye of the userand the image-light generating unit for the left eye of the user executethe emission of the image light, wherein in the power saving state, thedisplay control unit transitions the image-light emission of theimage-light generating units among a first state in which only theimage-light generating unit for the left eye of the user emits imagelight, a second state in which only the image-light generating unit forthe right eye of the user emits image light, and a third state in whichboth the image-light generating units for the left eye of the user andfor the right eye of the user emit image light, the condition set inadvance is a condition that the difference between the temperaturedetected by the temperature detecting unit for the right eye of the userand the temperature detected by the temperature detecting unit for theleft eye of the user is equal to or larger than a predeterminedtemperature difference, and when a switching condition is satisfied, thedisplay control unit is configured to transition the image-lightemission of the image-light generating units from the first state to thesecond state through the third state, when a first condition isselected, the display control unit is configured to transition theimage-light emission of the image-light generating units from equallybetween the first state and the second state, and when a secondcondition is selected, the display control unit is configured totransition the image-light emission of the image-light generating unitsfrom one of the first state and the second state to the other of thefirst state and the second state.
 16. The head-mounted display deviceaccording to claim 15, wherein the virtual image made in the powersaving state by one of the image-light generating unit for the right eyeof the user and the image-light generating unit for the left eye of theuser display in the virtual field of the user is the same as the virtualimage displayed in the normal state.